A starting point for the invention has been a centrifugal separator, which has a rotor for rotation around a central axis extending through the rotor and in which
a rotor body, which comprises a first end wall and a second end wall arranged axially one on each side of a separation chamber surrounding the rotor axis, forms a central inlet for said liquid containing the suspended light and heavy particles, a central first outlet through said first end wall for liquid having been freed from light and heavy particles, and a central second outlet for a liquid light phase containing separated light particles, PA1 a stack of conical separation discs is so arranged in the separation chamber that the separation discs, which have base portions and apex portions and which are arranged with interspaces between themselves, are placed coaxially with the rotor and have their apex portions facing said first end wall, PA1 each one of several inlet channels, which are distributed around the central axis and which connect the central inlet of the rotor body with the separation chamber, has an inclination relative to the central axis in the same direction as a generatrix of each one of said conical separation discs, PA1 the separation discs have several series of aligned holes forming several parallel distribution channels through said stack, which communicate with the interspaces between the separation discs and at their ends closest to said first end wall communicate with said inlet channels, PA1 each one of a number of outlet channels, which are distributed around the rotor axis and intended for liquid having been freed from light and heavy particles, has a channel opening situated in the separation chamber in the vicinity of said first end wall at a level radially outside the stack of separation discs and extends from this channel opening towards the central axis of the rotor, and PA1 the rotor is substantially free of entrainment members in a flow space in the separation chamber situated radially outside and surrounding the stack of separation discs, so that liquid leaving the interspaces between the separation discs is allowed to rotate at an angular speed smaller than that of the rotor body while it flows towards said channel openings. PA1 that said inlet channels open in a counter pressure chamber, which extends around the rotor axis and is delimited axially by chamber walls which are substantially free of rotational entraining members, so that liquid is allowed to rotate in the counter pressure chamber at an angular speed smaller than that of the rotor body, PA1 that the counter pressure chamber has a first portion, which communicates with said distribution channels, and a second portion which is situated radially outside said first portion and communicates with at least one sludge passage, and PA1 that the sludge passage opens in the separation chamber at a level radially outside the stack of separation discs.
A centrifugal separator of this kind, known for instance from SE-19 666 and SE-21 885 (both granted in 1904), has certain advantages over other centrifugal separators. One advantage lies in the fact that liquid to be treated in the centrifugal separator is introduced into the rotor separation chamber at the rotor end wall, towards which the separation discs turn their apex portions. This makes possible an effective use, from a separation point of view, of said inlet channels which extend between the central inlet of the rotor and the so called distribution channels in the stack of separation discs. Thus, thanks to the inclination of these inlet channels in relation to the rotor axis, the pre-separation of liquid obtained in the inlet channels may be used to a maximum, i.e. the result of this pre-separation is not spoiled by an undesired cross flow of the part flows of liquids, which are obtained through the pre-separation, when the liquid is conducted further on into said distribution channels. Such cross flow would be obtained, however, if the liquid would be conducted into the distribution channels at the opposite end of the separation disc stack after having flowed through corresponding inlet channels having the same inclination relative to the central axis in this part of the rotor.
Another advantage of a centrifugal separator of the defined kind is that liquid being conducted into the separation chamber in the described manner can, advantageously, be introduced into the rotor at the rotor body end wall at which said inlet channels are situated. Thus, the liquid need not be conducted axially through the whole of the rotor before it enters the separation chamber, which today most often occurs in centrifugal rotors having frusto conical separation discs. This is advantageous particularly in connection with rotors having relatively small dimensions and having both of their respective end walls kept axially together by means of force absorbing members arranged centrally in the rotor.